The production of gasoline according with the new European Environmental Standards requires that the refiners to lower the sulfur content in gasoline to values that are lower than 50 ppm since 2005. For example in Germany the content of sulfur in gasoline should be lower than 10 ppm. For the case of USA the content of sulfur is limited to lowest than 80 ppm and with average of 30 ppm. In attention to this claims, PEMEX Refining should be produce gasoline with sulfur content between 15 and 30 ppm for the years 2008-2010.
The classic method used for sulfur removal in Refining Processes is the catalytic Hydrodesulfurization (HDS technology) at high temperature and pressure. This method is very costly process that required drastic operation conditions and it is inefficient to reduce aromatic sulfur compounds especially for Mexican heavy crude oil, so is more reasonable the use of alternative desulfurization process. For increasing the efficiency of HDS process some technology modification are required such as the addition of other catalytic bed, more efficient catalyst, higher temperature and pressures and to reduce LHSV to expense of few processing capacity.
New technologic lines have been develop on in several countries in order to resolve this problem (Zaczepinski, S. Exxon, Diesel Oil Deep Desulfurization (DODD) in Handbook of Petroleum Refining Processes, ed. R. A. Meyer, McGraw-Hill, NY, 1996, Ch. 8.7), i.e.: the absorption of sulfur compounds over solid absorbents, like IRVAD® process (U.S. Pat. No. 5,730,860, dated Mar. 24, 1998) from Black & Veatch Pritchard Inc.; the process S-Zorb® from Phillips Petroleum, the process Haldor Topsoe (EP 1057879, dated Dec. 6, 2000); and the liquid-liquid extraction with volatile organic solvents (Petrostar Refining, 217 National Meeting, American Chemical Society, Anaheim, Calif., March, 1999). An original process is the oxidative desulfurization with different oxidant agents (Unipure Corp., NPRA Meeting No AM-01-10, March 2001; Sulphco Corp, NPRA Meeting No AM-01-55, March 2001; BP Chemicals UK, Journal of Molecular Catalysis A: Chemical (1997) 397-403; UOP LLC, U.S. Pat. No. 6,171,478, dated Jan. 9, 2001; EXXON Research and Engineering Co., U.S. Pat. No. 5,910,440, dated Jun. 8, 1999; U.S. Patent Publication No. 2002/0035306 A1 with publication date of Mar. 21, 2002; U.S. Pat. No. 6,596,914 B2, dated Jul. 22, 2003; U.S. Pat. No. 6,406,616, dated Jun. 18, 2002 and U.S. Pat. No. 6,402,940 B1 dated Jun. 11, 2002; Fuel 82 (2003) 4015; Green Chemistry 5 (2003) 639). Recently the extraction of sulfur-containing compounds using liquid-liquid extraction employing ionic liquids has been welcome by scientific community.
Ionic liquids are known for more than 30 years, but their industrial applications began in the last 10 years (Rogers, R. D.; Seddon, K. R (Eds.), Ionic Liquids: Industrial Applications of Green Chemistry, ACS, Boston, 2002). They are applied as solvents and catalyst in alkylation reactions, polymerization and Diels-Alder cycloaddition. In addition they are employed in electrochemical processes, in supercritical CO2 extraction of aromatic compounds and sulfur compounds in hydrocarbon mixtures. One of the first publications mention the use of ionic liquids for the removal of mercaptans (WO 0234863, dated May 2, 2002). The patented method is based on the use of sodium hydroxide in combination with ionic liquids for the conversion of mercaptans to mercaptures, which were removed using ionic liquids. Peter Wassercheid and coworkers published several papers and patents between 2001 and 2005 about the use of ionic liquids for desulfurization of gasolines (Chem. Comun. (2001) 2494; WO 03037835, with publication date of 2003-05-08; U.S. Publication No. 2005/0010076 A1, published Jan. 13, 2005). In these works the authors employed ionic liquids with C+ being 1,3-dialkylimidazolium or tetralkylammonium, and A− being tetrachloroaluminates or methanesulfonates. By means of a process with several extractions (up to 8 extractions), high extraction of sulfur compounds were achieved using model gasolines. However these kinds of compounds are air and moisture sensitive and a polymerization reaction was observed during the extraction process. U.S. Patent Publication No. 2003/0085156 A1 published May 8, 2003 and U.S. Pat. No. 7,001,504, dated Feb. 21, 2006, also mention the use of ionic liquids, where C+ is an ammonium o fosfonium and quaternary, A− being tetrachloroaluminates for the extraction of sulfur from model gasoline. In the paper published in Energy & Fuels 18 (2004) 1862, the use of ionic liquids containing Copper chloride (I) anion with the same application, and in the papers Ind Eng. Chem. Res. 43 (2004) 614 and Ind. Eng. Chem. Res. 46 (2007) 5108-5112) several ionic liquids were evaluated for the extraction of sulfur and nitrogen-containing compounds. More recently, some papers (Energy & Fuels 20 (2006) 2083-2087; Green Chemistry 8 (2006) 70-77; Progress in chemistry 19 (2007) 1331-1344; Green Chemistry 10 (2008) 87-92) also report the use of IL for desulfurization processes. U.S. Patent Publication No. 2004/00445874 A1, published Mar. 11, 2004, discloses a procedure for desulfurization and denitrogenation of hydrocarbons fractions using a wide family of ionic liquids and alkylations agents with high efficiency in some cases.